I have comfort access in my 07 335i. Problem is that it doesn't work when I try to unlock the car after the car has gone to sleep. I can press the unlock on the key fob and that will unlock the doors. Also, if the car is "awake" comfort access seems to work. Coming back to my car after work, however, comfort access never works.

Reading the forums, it sounds like my battery is draining and the car is going to sleep. I do get a low battery warning after a few minutes if the engine is off but the car is still on, so I am pretty sure that there's a battery problem of some kind.

I have a jb4, so not sure if that is causing the issue, although Terry @ BurgerTuning says it's not.

Curious if anyone knows what might be going on. About to take to the dealer, but have to remove the JB4, and it was a pain to install.

Car battery ever been replaced?
If not I'd say that. Your symptoms are exactly like mine were. If I had just opened car with FOB the CA would work.
If car had been sitting overnight etc it would not. When the battery starts going the car starts disabling unnecessary systems such as CA to conserve battery. So if car is "asleep" it will no longer
look for your keyfob being in proximity.

I had to replace battery and clear codes that put it into this power save mode using BT tool and also register new battery.

After getting a low battery warning on my (unmodded) '07 E91 about a year ago, my dealer found no problems - until the tech tried to restart the car and had difficulty doing so. After throwing a couple of alternators at it (thank you, OEM warranty!), an intermittent fault with the IBS was found so it was replaced.

Everything worked fine for about 8 months, but I'm now having the same problem as the OP. About every 3rd day, the CA will not unlock the doors and the low battery warning appears when keeping the ignition on while parked. And once or twice, the missing key icon flashed and the car would not start without inserting the fob. The rest of the time CA works as it should. When the dealer recently checked the battery & charging system, everything was found to be OK, but every third day or so, the problem returns.

Since 2/3 of the time, CA functions normally and there are no warning icons, I'm reluctant to replace the battery. It seems as if some sensor is intermittently sending a spurious low battery message for some reason.

OP, unless I can get mine to the dealer while it is "acting up", I will be curious to hear how your situation works out.

Sorry to high jacked this tread.I have the same issue and my car is in the dealer(been there for a week all ready). CA is not working ones the car goes to sleep(15 minutes after locking).They have replace the + battery cable and the fuse box, do to car shutting down while driving and having no power in the whole car in 2 occasion .They have also replace the car battery and remote control batteries and still CA not working after car goes to sleep.

They have replace the car handle and no luck.They have reprogram the car (?) and still not working. They are keeping it at the dealer because they are waiting for a BMW technician to come down and take a look at it on Monday.I had jb3 in car and took it out in Oct 2011 and all my other mods (back up camera). There is something big going on with my electrical system.

This is a list of my electrical issue since Oct 2011
1.nav screen replace no image
2.sat unit replace not working
3.radio dead wouldn't turn on replace
4.jb unit replace do to electrical acting up
5.L7 amp replace do to no sound
6.instrumental display replace do to speedo and tach not working
7.start stop switch replace do to not working
8.all door lock motor replace
9. all windows motor also replace

Sorry for the long reply, but the dealer knows me by name and said that they are going to put my name on one the parking space. I have 69k miles and it's a 2007 335xi.It's being in the dealer for 65 days since Oct 12 2011. Good thing is that I purchase there 7yrs/100k miles warranty and everything has been under warranty.I will keep you posted once they let me know.

I discovered the exact same problem you are having last night in my '08 335i. The CA has been working intermittently for some time, but i always thought i was doing it wrong. LOL

It sometimes locks but doesn't unlock after that, and the key battery discharged message appears on the dash. Yesterday it wouldn't start without the fob in the dash at all when i had it on just a few minutes before that.

I have comfort access in my 07 335i. Problem is that it doesn't work when I try to unlock the car after the car has gone to sleep. I can press the unlock on the key fob and that will unlock the doors. Also, if the car is "awake" comfort access seems to work. Coming back to my car after work, however, comfort access never works.

Reading the forums, it sounds like my battery is draining and the car is going to sleep. I do get a low battery warning after a few minutes if the engine is off but the car is still on, so I am pretty sure that there's a battery problem of some kind.

I have a jb4, so not sure if that is causing the issue, although Terry @ BurgerTuning says it's not.

Curious if anyone knows what might be going on. About to take to the dealer, but have to remove the JB4, and it was a pain to install.

If the car thinks the car battery is low (whether it is or not ... A faulty ibs cable can report low voltage erroneously), comfort access is one of the first functions to be degraded in order to conserve battery. But once the car "wakes up" by unlocking with a fob for example comfort access functions are typically restored.

I had this problem but also bad intermittent lock and unlock when the car was fully "awake". Diversity antenna and tint replacement to ceramic seemed to fix it. This was under warranty and "goodwill" by BMW.

Troubleshooting comfort access problems is difficult. A variety of subsystems, signal paths, and handshaking are used. Faults are not always reported when the comfort access function is not working properly. And getting a BMW dealership to work on a problem that doesn't have a corresponding fault being reported can be difficult and may require BMWNA authorization. I'm speaking from my own personal experience.

If the problem is electromagnetic interfence (EMI) in nature, a fault will not always be reported. An example would be if the system is not recognizing your remote because RF signals sent or received are too low or degraded due to multipath interference (RF reflections which can can add or subtract or deteriorate a digital signal), environmental loss (e.g. tint), insufficient antenna gain at transmit and/or receive location . A certain design threshold must be exceeded for a signal to be processed correctly in any system which includes RF signals as a component. If the signal is inadequate, the system may not work properly or may not work consistently.

You could narrow the problem down to electromagnetic in nature if you observe different behavior say in the garage versus out in the open. I found that my comfort access would work reliably in my garage or an enclosed space but not in the open (say in a street or parking lot). I also found "dead zones" where if I held out the remote in one spot comfort access worked but in another spot it would not. These are indications of EMI or signal loss.

I would always suggest the first, easiest thing to try as a fix if you're experiencing comfort access problems is simply to swap out battery in your remote with a new one. Beyond that, things can get much more complex to diagnose and fix.

Faulty IBS sensor in the negative battery cable could be incorrectly reporting a low car battery voltage which could cause comfort access not to be available until the car is "awake". A fault code should be generated if the IBS is not functioning correctly, but you may not get a dash failure indication or the iDrive "Increased Battery Discharge message".

If comfort access has been disabled to conserve the car battery, whether it's an actual low voltage or a false low voltage due to bad IBS sensor, comfort access using the door handle capacitive sensor button will not work while the car is asleep.

But if it's an RF signal-related issue comfort access will work intermittently or on the passenger side but not the driver side door handle button when the car is asleep. I also found if on the driver's side I took one step towards the back of the car it would work. Presumably this was because I was closer to the diversity antenna near the rear brake light in the back window (for E90 335i) which is used in the detection of the remote transmitter for a car that is asleep.

I have been having similar problems with my M3, over the last few months.

I would either get "key discharged" type error messages, with the picture between the tach and speedo, or "key not present" messages.

Up to last week, the only real problem would be that the driver's side door handle would not respond (note that this is right hand drive) whereas the passenger's would. The boot lid would refuse to respond to multiple presses.

So inconvenient but just annoying.

I changed the battery in the key fob, but no change in symptoms.

I booked the car into the local dealer for diagnostics, and on the day that I was taking it in, the car refused to start, unless I put the key in the slot.

So, the dealer takes a look and says that it is the main (car) battery which is a bit low, and they put it on charge for half a day, expecting to solve the problem (I did not have any confidence in this).

I go to pick the car up from the dealer, and soon as I switch on the ignition, the key discharged symbol appears again....sigh....but the car does start.

No non-standard tints, car completely as it left the factory.

Now they want to check it again, and probably start changing door handles (which will need to be painted, Mineral White....impossible to match....) whereas I think it has to be the base-station transmitter.

I bought a 2012 E92 a couple of weeks ago. Comfort Access worked like a champ, and the suddenly quit working. Keyless start worked fine, but door handles and trunk quit working without the key FOB unlock/lock buttons being pressed? I dunno why, operator error I am sure. So a little searching found this. Typically this malfunction occurs because you started the car, and then walked out of range of the sensor with the key fob. If that happened this procedure might re-enable your Comfort Access in the door handles:

Like I said, I dunno why for sure, but this was my situation... Time will tell. Could've been my switchology. Had a couple of instances where it didn't recognize the key while it was in my pocket. All I do know, is the above procedure "reset" my CA